1. Field of the Invention
The present invention relates to a composite piezoelectric component such as a composite trap including a plurality of piezoelectric resonant elements, and more specifically, the present invention relates to a composite piezoelectric component having a structure in which a plurality of piezoelectric resonant elements are stacked and joined to each other via conductive joining members.
2. Description of the Related Art
Various composite piezoelectric components formed by electrically connecting a plurality of piezoelectric resonant elements are known.
For example, Japanese Unexamined Patent Publication No.4-192909 discloses a composite trap as an example of such composite piezoelectric components. As shown in FIG. 6, this composite trap 61 includes a first trap element 62 formed of double-mode ceramic resonators having the same resonant frequencies and a second trap element 63 formed of double-mode ceramic resonators having resonant frequencies which are different from each other. The first trap element 62 and the second trap element 63 are mounted on a rectangular-shaped base substrate 64.
The first trap element 62 and the second trap element 63 are electrically connected to each other by electrodes provided on the base substrate 64. Furthermore, lead terminals 65 to 67 are joined to the electrodes on the base substrate 64. The entire composite trap except for a portion to which the lead terminals 65 to 67 are extended is covered by an exterior resin as shown by phantom lines xe2x80x9cAxe2x80x9d.
In the composite trap 61, since the two elements, i.e., the first trap element 62 and the second trap element 63, are mounted next to each other on the base substrate 64, the overall size of the trap 61 is very large.
Japanese Unexamined Patent Publication No.4-192909 also discloses a composite trap having the first and second trap elements 62 and 63 stacked on each other and joined via a conductive joining member and a plurality of lead terminals connected thereto, and covered by an exterior resin. A special shaped lead terminal is used and arranged so as to be electrically connected to each terminal electrode to be connected to a ground of the first and second trap elements 62 and 63, having branches in the sides to be connected to the first and second trap elements 62 and 63. That is, each branch portion of the lead terminal is connected to each terminal electrode used to establish a ground for the first and second trap elements 62 and 63.
The composite trap requires the special shaped lead terminal which increases the cost and requires very difficult assembly processes.
On the other hand, Japanese Unexamined Patent Publication No.6-326546 discloses a composite piezoelectric component 71 shown in FIG. 7. In this component, a plurality of piezoelectric substrates 72 and 73 are bonded together via adhesives 74.
FIGS. 8 and 9 are perspective views showing electrodes formed on the top surface and the bottom surface of the piezoelectric substrate 72, respectively. On the top surface of the piezoelectric substrate 72, vibrating electrodes 75 and 76 are provided. On the bottom surface of the piezoelectric substrate 72, vibrating electrodes 77 and 78 are arranged so as to oppose the vibrating electrodes 75 and 76 at the front and the back with the piezoelectric substrate 72 disposed therebetween. A first piezoelectric vibrating unit is defined by the vibrating electrodes 75 and 77 while a second piezoelectric vibrating unit is defined by the vibrating electrodes 76 and 78. Similarly, two piezoelectric vibrating units are also included in the piezoelectric substrate 73.
On the one side edge of the piezoelectric substrate 72, a plurality of notches 72a to 72c are provided. Extending electrodes 79 and 80 are connected to the vibrating electrodes 75 and 76 so as to extend therefrom toward the insides of the notches 72a and 72c, respectively. An extending electrode 81 to be electrically connected to the vibrating electrodes 77 and 78 is disposed on the bottom surface of the piezoelectric substrate 72. The extending electrode 81 is arranged to extend to the inside of the notch 72b and in turn to extend toward the top surface of the substrate across the notch 72b. 
In the composite piezoelectric component 71, the above-mentioned piezoelectric substrate 72 and the piezoelectric substrate 73 are joined together, although as for the piezoelectric substrate 73, the top surface thereof is the surface on which the vibrating electrodes 77 and 78 are disposed.
In the composite piezoelectric component 71, the piezoelectric substrates 72 and 73, each having two piezoelectric vibrating units, define a composite unit by being joined together. Since the two piezoelectric substrates 72 and 73 are deposited on each other to define the composite unit, the composite piezoelectric component having plural piezoelectric elements is miniaturized.
However, for the purpose of achieving the electrical connections of the two piezoelectric elements, i.e., the piezoelectric vibrating units disposed on the piezoelectric substrate 72 and 73 and the electrodes to be electrically connected to a ground, the above-mentioned notches 72a to 72c are used. That is, electrical connections are achieved by stacking the piezoelectric substrates 72 and 73 on each other such that the notches formed on the side edge of the piezoelectric substrate 72 are positioned on the corresponding notches formed on the side edge of the piezoelectric substrate 73 and then by forming electrode thin-films inside the notches via vapor deposition, sputtering, or other methods.
Therefore, the extending electrodes 79, 80, and 81 must be extended from the piezoelectric vibrating units to the notches 72a to 72c formed on the side edge. As a result, the sizes of the piezoelectric substrates 72 and 73 must be large.
In addition, this structure causes the reliability of the electrical connections to be insufficient. Consequently, breaking of the electrode thin-film is liable to occur at the edge portion facing to the notch.
Furthermore, in the composite piezoelectric component 71, the vibrating electrodes 75 and 76 are exposed on the top surface thereof. Therefore, in order to protect the piezoelectric vibrating units, a case member, or other protective member, must be disposed on the top surface of the composite piezoelectric component 71 so as to secure spaces for allowing for free vibration of the piezoelectric vibrating units, which prevents any reduction in the thickness and overall size of the component.
To overcome the above described problems, preferred embodiments of the present invention provide a composite piezoelectric component including a plurality of electrically connected piezoelectric elements, which achieves a significant reduction in size and a great increase in the reliability of electrical connections of the plurality of piezoelectric elements by solving the above-described problems of conventional techniques.
According to one preferred embodiment of the present invention, a composite piezoelectric component includes a plurality of piezoelectric resonant elements each including a substrate having a first major surface and a second major surface disposed opposite to each other, a pair of vibrating electrodes disposed on the first and second major surfaces, respectively, so as to oppose each other with the substrate disposed therebetween, a ground electrode connected to ground and disposed on at least one of the first and second major surfaces, and each of the plurality of piezoelectric resonant elements being stacked on each other so that the major surface of one substrate opposes the major surface of another substrate, a conductive joining member electrically connecting at least two of the vibrating electrodes and the ground electrode of the plurality of piezoelectric resonant elements and mechanically bonding the deposited piezoelectric resonant elements, each of the substrates of one of the piezoelectric resonant elements other than the piezoelectric resonant element deposited on the top portion including a plurality of piezoelectric substrate portions, a conductive material portion arranged between the plurality of piezoelectric substrate portions, the ground electrodes being provided on the first and second major surfaces of the substrate in the conductive material portion, and the plurality of ground electrodes of the piezoelectric resonant elements being electrically connected to one another via the conductive material portion and the conductive joining members.
In the above described composite piezoelectric component, the conductive material portion may be arranged substantially in the center of the substrate.
Also, at least one of the plurality of piezoelectric resonant elements may be a first trap element defined by a double-mode ceramic resonator, and at least one of the plurality of piezoelectric resonant elements may be a second trap element defined by a double-mode ceramic resonator having a resonant frequency that is different from that of the first trap element.
Further, each of the first and second trap elements may include two pairs of vibrating electrodes disposed on the first and second major surfaces, respectively, so as to oppose each other with the substrate disposed therebetween, and a ground electrode disposed on at least one of the first and second major surfaces of the substrate. The ground electrode is electrically connected to the vibrating electrodes disposed on the same surface and a terminal electrode is electrically connected to the vibrating electrodes which are not connected to the ground. The substrate of the trap element deposited at the bottom side in the first and second trap elements preferably includes first and second piezoelectric substrate portions and the conductive material portion arranged between the first and second piezoelectric substrate portions. The ground electrode is disposed on the first and second major surfaces of the substrate in the conductive material portion. The corresponding terminal electrodes of the first and second trap elements are electrically connected to each other.
The above described composite piezoelectric component may further include a lead terminal joined to the terminal electrode and a lead terminal joined to the ground electrode.
A composite piezoelectric component according to another preferred embodiment of the present invention may be a component having two terminals or may be a chip-type component.
That is, according to preferred embodiments of the present invention, a composite piezoelectric component preferably includes lead terminals joined to the terminal electrodes and a lead terminal joined to the ground electrode.
Another preferred embodiment of the present invention provides a chip-type composite piezoelectric component including a first case member on which a plurality of external electrodes are disposed, the composite piezoelectric component being mounted on the first case member, and a second case member connected to the first case member so as to surround the composite piezoelectric component mounted on the first case member.
In the composite piezoelectric component according to preferred embodiments of the present invention, a plurality of piezoelectric resonant elements are joined together and the ground electrode disposed on the bottom surface of the top piezoelectric resonant element is electrically connected to the ground electrodes located on the other piezoelectric resonant elements via the conductive joining members and the conductive material portions in the depositional direction. That is, only when plural piezoelectric resonant elements are joined together via the conductive joining members, the ground electrodes of plural piezoelectric resonant elements are securely electrically connected to each other.
Accordingly, at least when the electrode for being connected to. a ground is connected, the extending electrode and other elements are not required, thereby enabling the composite piezoelectric component to be miniaturized. The electrical connections of piezoelectric resonant elements are performed by utilizing the conductive joining members, and the conductive joining members make surface contact with a pair of electrodes to be joined, so that the reliability of electrical connection is greatly improved.
Therefore, a small-sized composite piezoelectric component having very reliable electrical connections is achieved.
According to preferred embodiments of the present invention, when the conductive material portion is arranged on the approximate center of the substrate, the substrate having the conductive material portion can be easily formed merely by cutting off a mother block which is obtained by deposition of the same shaped piezoelectric blocks via a conductive material.
When the plural piezoelectric resonant elements are defined by a first trap element including a double-mode piezoelectric resonator having the same resonant frequencies and a second trap element including a double-mode piezoelectric resonator having resonant frequencies different from those of the first trap element according to preferred embodiments of the present invention, a very small composite trap having very reliable electrical connections is achieved.
When each substrate of the trap element deposited in the bottom side in the first and second trap elements includes a first and a second piezoelectric substrate portion, and the conductive material portion arranged between the first and second piezoelectric substrate portions, and when the ground electrodes are located on the both principal surfaces of the substrate in the conductive material portion and the corresponding terminal electrodes of the first and second trap elements are electrically connected to each other, electrodes for being connected to a ground of the first and second trap elements are electrically connected to each other via the conductive joining members and the conductive material portions, thus, enabling the composite trap to have greatly improved reliability of the electrical connections and also to have a greatly reduced size.
When the composite trap includes a lead terminal connected to the terminal electrode and a lead terminal connected to the ground electrode, the composite piezoelectric component according to various preferred embodiments of the present invention provides an electronic component with leads.
When the composite piezoelectric component includes a first case member having a plurality of external electrodes disposed thereon, a composite piezoelectric component according to preferred embodiments of the present invention mounted on the first case member, and a second case member joined to the first case member so as to surround the composite piezoelectric component mounted on the first case member, this component is easily surface-mounted on a printed-circuit board or other substrate. Moreover, a very small chip-type composite piezoelectric component having very reliable electrical connections is provided.
Other elements, features, characteristics and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention which refers to the accompanying drawings.